B 、 PHYSICAL AND CHEMICAL ROPERTIES OF PRODUCT ：The product exists in form of white powder of monoclinic crystals with strong SO 2 smell when being wet, but without any other smell after it is dried. Its relative density is 1.48 . It is easy soluble in water and little soluble in ethanol. It disintegrates easily when being heated. Its water solution exhibits acidity with strong reducibility. It is easily oxidized in air or loses its sulfur dioxide. It is made by introducing sulfur dioxide into sodium hydroxide or sodium acid carbonate.

E 、 CAUTION ：The product is very easy to be oxidized when exposed to air and emit sulfur dioxide continuously, so it is difficult to store the product for a long time in open air and it is necessary to protect the product from moisture. The product will disintegrate when heated above 150 ℃ and emit sulfur dioxide gas, so the product cannot be stored and transported together with gasoline, acids or oxidants and other inflammable substances. The product is packed in internal plastic bags with external braided bags in net weight of 50kg . Product for export is packed in net weight of 25kg .